Testing method for non-destructive testing of a welded connector, a testing device and an ultrasonic welding apparatus having such a device

ABSTRACT

In testing a method for non-destructive testing of a welded assembly which includes a plurality of strands of electrical conductors which are joined together into a bundle by ultrasonic welding, a defined testing force is introduced into two or more shell surface segments of the welded assembly in directions oriented substantially towards each other or substantially to a comon intersection. For carrying out the testing method, a testing device and a welding machine which constitute such a testing device are provided.

FIELD OF THE INVENTION

The invention relates to a non-destructive method of testing a weldcomprising a plurality of strands of electrical conductors joinedtogether into a bundle by ultrasonic welding. Furthermore the inventionrelates to a testing apparatus for implementing the cited test methodand to an ultrasonic welding machine having such an apparatus.

“Weld” in this context covers any welded connection comprising, moreparticularly, the following properties. Firstly, two or more strippedstrands are joined together by an ultrasonic welding method. It isunderstood that a strand of an electrical conductor or cable comprises aplurality of single wires. The single wires are designed to conduct anelectrical current and are normally made of copper or some othermaterial as generally appreciated in the field concerned. Ultrasonicwelding is characterized by each of the single wires to be joinedtogether being heated up by vibration, disrupting the surfaces of thesingle wires, smoothing out surface irregularities and thus achieving aweld. The stripped strands are typically arranged parallel to each otherand then welded to each other cylindrically by some kind of section overa predetermined length. More particularly, jointing is also promoted bythe single wires being crimped together.

PRIOR ART

Welds of the aforementioned kind need to be fabricated very often inproducing wiring harnesses. These can be wiring harnesses for motorvehicles, commercial vehicles as well as for components for aircraft andmarine applications. In producing a wiring harness on a so-called makeupboard a weld is produced directly in the wiring harness by an ultrasonicwelder in creating an electrical connection between several electricalconductors.

If inspection were to find a weld to be insufficient or unsatisfactory,i.e. failing to produce a satisfactory electrical connection or lackingin mechanical (bonding) strength when the wiring harness has alreadybeen installed, the entire damaged wiring harness would need removing asa whole and to be replaced new. This is prohibitively costly andtime-consuming. Accordingly, it is especially in just-in-time productionin automotive engineering not permitting any delay, that it isunacceptable for wiring harnesses to be installed with faulty or NO GO(defective) welds.

This is why attempts have been made to develop test methods which permittesting the welds (welded connections) produced prior to the wiringharnesses being installed. However, to date only tests could beimplemented which involve destroying the weld. For this purpose peel orbending tests have been developed, pull tests implemented andmicrographs analyzed. For one thing, this is unacceptable economicallysince this also involves destroying GO welds at great expense. Foranother, this test method can be carried out naturally only on asampling basis, thus risking NO GO wiring harnesses being installed.

It is due to this that attempts have already been made to check thewelding properties already in the ultrasonic welding machine. For thispurpose an internal quality control, a so-called inspector was installedin the system for monitoring a plurality of trouble sources such as forexample oxydized conductors, grease or oil inclusions in the weld,copper quality. In addition the weld is gauged to establish its degreeof density from the ratio of height to width. However, this test methodis also complicated and inaccurate.

Attempts have also been made to obtain an indication as to the qualityof the weld already during welding by testing its ring in sound. Thisinvolves simulating various factors having a negative influence on theweld. But this method too, failed to lead to any positive result. Alsoinvestigated was the possibility of a ultrasound or eddy current testsince these methods are already put to use in checking for inclusions incastings or for welding seam quality assessment. However, thiscomposition bears no comparison with those in a weld of theaforementioned kind since unlike welded strands a solid structure isinvolved, thus making it relatively easy to analyze the quality.

SUMMARY OF THE INVENTION

The technical problem on which the invention is based involvescomprising a method of non-destructively testing a weld of theaforementioned kind which is simple and reliable in application, also inaccompanying the process to permit obtaining a certain indication as tothe strength and electrical conductivity of the weld.

This technical problem is solved by a test method having the features ofclaim 1. The non-destructive test method in accordance with theinvention is characterized in that a defined testing force is introducedinto two or more shell surface segments of the weld in directionsoriented substantially towards each other or substantially to a commonintersection.

The gist of the invention is based on applying a pressure to thestructure of a weld of the aforementioned kind such that should a NO GOweld be involved a discernible change occurs, whereas a GO weld resultsin no such change and thus there is no destruction of the weld. For thefirst time it is now possible in accordance with the invention to makeuse of the “uncoiling” of the wires making up the strands of electricalconductors welded to each other only superficially occurring only withslight pressure loading when the weld is a NO GO.

From exhaustive tests it has been discovered that the difference betweenthe defined testing force and the force at which a fault already occurswhen the weld is a NO GO is relatively large. Thus, the force needed totest a GO weld is roughly 2.5 to 1.25 times the force needing to beapplied to produce a discernible change for a NO GO weld. For example, aforce of 1,000 N turned out to be sufficient as the testing force fornon-destructively testing a weld made up of copper single wires having awidth of 2.8 mm and a height of 2.1 mm with a ram to anvil length of 6.5mm.

The testing force to be applied depends, of course, on thecross-sections, size and material of the single wires making up thestrands of the electrical conductors as well as on the welded conditionsset on the ultrasonic welding machine. However, in accordance with theinvention a method of non-destructively testing such a weld is now madeavailable for the first time which is defined by a pressure test. Forthis purpose it is, of course, necessary that the testing force isapplied as best possible without notching the weld and that, inaddition, sufficient clearance remains at the periphery of the weld sothat a NO GO weld produces an uncoiling effect and thus a “bloating” ofthe single wires for observation. This means that the nesting jawssuitable, for example, for applying the testing force in a testingapparatus do not cover the full shell circumference. Due to this it is agreat advantage when the defined testing force is applied as anelongated load substantially along shell lines or narrow shell surfacesegments of the weld.

Due to the fact that the testing force is increased continuously from alow starting value to a defined testing force, especially in a linearincrease, any commencement of a NO GO or uncoiling of the single wiresin the weld is very quickly discernible. More particularly, when theforce profile is plotted and analyzed any NO GO can be very quicklysensed and alerted as desired, for example, by a visual or audibleindication.

As already explained, the defined testing force depends on the type ofweld involved and on the conditions in ultrasonic welding. However, ingeneral it can be said that the defined testing force is 2.5 to 1,25times higher than the force resulting in a first discernible change in aNO GO weld.

Welds of the aforementioned kind are generally configured square orround in cross-section. Where such welds are concerned, applying theforce is preferably done to two opposing longitudinal edge portions.Where oval or elliptical cross-sections are involved the force iscorrespondingly applied to opposing main or ancillary apexes. In thesame way, where symmetrical cross-sections are involved the force isapplied to advantage to opposing shell surface segments in the region ofthe longitudinal centerline. Otherwise, of course, applying the force totwo or more longitudinal edge portions or general shell surface segmentsis possible and expedient.

An apparatus for implementing the aforementioned test method comprisesthe features as set forth in claim 11. This apparatus is characterizedby two or more nesting jaws movable in directions oriented substantiallytowards each other or on a common intersecting direction, each of whichis formed so that a weld to be tested is nested along a shell surfacesegment. In addition a means is needed for squeezing the nesting jawstogether with a defined testing force which is so high that nodisruption results with a GO weld whereas a discernible change occurs ina NO GO weld.

For this purpose the nesting jaws may be configured greatly differinglyto comply with the cross-sections of the weld to be tested. For example,a wedge shape is suitable with or without a parallel arrangement ofscores, notches or the like on the faces contacting the weld. However,concave or convex nesting jaws, especially of round or ovalcross-sections, are also expedient.

In one preferred embodiment of the testing apparatus a means of limitingthe testing force is provided to restrict the testing force capable ofbeing applied as a maximum. The testing force is adaptablecorrespondingly to the nature of the weld to be tested.

In principle any NO GO condition of the weld may be discerned visuallysince an “uncoiling” occurs in such a NO GO condition, resulting in theouter shape of the test object changing. To advantage, however, a meansof sensing the change, for example in the form of a strain gauge, forcesensor or the like is provided with which the change occurring in thecase of a NO GO weld can be sensed. This may also be, for example, adisplacement sensor. It is on the basis of of an alert signal output bythe sensing means that a visual and audible alert indication is given.

Applying the force is done preferably pneumatically or hydraulicallyassisted, but may of course also be applied manually in the case ofsmall cross-sections or small testing forces.

By incorporating such a testing apparatus in or directly at the outputof an ultrasonic welding machine for welding a plurality of strands ofelectrical conductors each made up of single wires into a weld ofpolygonal, round or oval cross-section, 100% testing can now beimplemented facilitated and cost-effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the invention will now be detailed for a betterunderstanding with reference to the attached drawings in which

FIG. 1 is a schematic side view of a weld to be tested comprising aplurality of strands of electrical conductors joined together into abundle by ultrasonic welding,

FIG. 2 is a schematic side view of a further configuration of a weld tobe tested,

FIG. 3 is a schematic illustration of a testing apparatus in accordancewith the invention, in this case test pliers, for non-destructivelytesting a weld of square cross-section,

FIG. 4 is a schematic illustration of the testing procedure for a squareweld,

FIG. 5 is a schematic side view of a testing apparatus in accordancewith the invention including a NO GO weld,

FIG. 6 is a magnified view of the NO GO weld as shown in FIG. 5,

FIG. 7 is a schematic view illustrating another configuration of thenesting jaws,

FIG. 8 is a schematic illustration of how the nesting jaws areconfigured for a round cross-section weld,

FIG. 9 is a further illustration of how the nesting jaws are configuredfor a round cross-section weld,

FIG. 10 is yet a further illustration of how the nesting jaws areconfigured for a round cross-section weld,

FIG. 11 is a schematic illustration of the test procedure for a weld oftriangular cross-section and showing the nesting jaws provided hereforas an example,

FIG. 12 is a view in perspective view of an end weld to be tested which,for a better Appreciation, is shown inserted in only one nesting jaw.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

The basic configuration of a weld 3 to be tested by a test method inaccordance with the invention for a GO weld is evident more particularlyfrom the FIGS. 1, 2 and 12. In principle, a weld 3 to be testedcomprises a plurality of stripped strands 2 of electrical conductors 1.Each strand 2 of an electrical conductor 1 is made up of a plurality ofsingle wires 6 as evident, for example, from the cross-section show inFIG. 4. Over the length L the individual strands 2 of the electricalconductors 1 or, more particularly, the single wires 6 of the pluralityof strands 2 have been joined together with an ultrasonic weldingjuxtaposed in parallel. This means that the individual strands 2 orsingle wires 6 “bond” to each other at the surface due to a combinationof vibration frequency and mechanical pressure. This results in a goodelectrical contact. It is usual that rectangular or squarecross-sections are formed in ultrasonic welding. However, of course,also round, oval, elliptical or also generally polygonal cross-sectionscan be produced.

Referring now to FIG. 1 there is illustrated a weld as a so-called endweld 3. An end weld 3 is characterized in that all stripped strands 2 ofthe electrical conductors 1 are located parallel to each other on thesame side of the weld 3. In contrast to this, in FIG. 2 there isillustrated a weld 3 in which the stripped strands 2 of variousconductors 1 run together from two face sides. But, these strands 2 too,are arranged parallel to each other.

Irrespective of the cross-section of the weld 3 both the electricalconnection of the weld and the mechanical strength need to be assured.Referring now to FIG. 3 there is illustrated test pliers in accordancewith the invention as may be used for this purpose, for example. Thetest pliers comprises an upper nesting jaw part 14 and a lower nestingjaw part 15. Integrated in the lower nesting jaw part is a display 13indicating the testing force. The upper nesting jaw part 14 and thelower nesting jaw part 15 are rotatively joined together via a hingejoint. Each upper nesting jaw part and lower nesting jaw part comprisesnesting jaws 11, 12 respectively.

In the example embodiment of the test pliers as shown in FIG. 3 thenesting jaws 11, 12 are configured wedge-shaped. The shape of the wedgeis selected so that the angle included therein is greater than thecorner angle of the weld 3. For testing, the weld 3 is inserted in thenesting jaws 11, 12 so that it applies the testing force to the diagonallongitudinal edges of the weld 3. For this purpose the nesting jaws 11,12 are moved towards each other. This is illustrated schematically inFIG. 4. A GO weld 3 produces no discernible, in this case visuallydiscernible, change when subjected to the testing force.

Referring now to FIG. 5 there is illustrated by contrast how the sametesting force produces a change in the weld 3 visually discernible, forinstance. The weld 3 is disrupted by the testing force applied via thenesting jaws 11, 12. An “uncoiling” of the single wires 6 of the singlestrands 2 connected on the surface to each other. This means the surfaceconnection of the single wires 6 of the strand 2 rupture; in the singlewires 6 “uncoil” from each other. A magnified illustration of this“uncoiling” action is better evident from FIG. 6.

Referring now to FIG. 7 there is illustrated a further aspect in theshape of the nesting jaws 11 a and 12 a. These nesting jaws 11 a, 12 acomprise several wedge-shaped grooves oriented parallel to each other.Each groove has an inner angle α which is larger than the outer angle ofthe longitudinal edge portions of the weld 3 to be gripped by thenesting jaws 11 a, 12 a. This results in the testing force beingintroduced merely via the opposing longitudinal edge portions into theweld 3 to be tested.

Referring now to FIG. 8 there is illustrated schematically the aspect ofnesting jaws 20, 21 for a weld 17 having a round cross-section. Theround cross-section weld 17 is made up of single wires 6 joined togetherby the ultrasonic welding method. To apply the testing force to the twoopposing narrow shell surface segments of the weld 17 each of thenesting jaws 20, 21 is configured concave. In this arrangement the radiiof the nesting jaws 20, 21 are selected larger than the radius of thecross-section of the weld 17 to be nested in the jaws.

Referring now to FIG. 9 there is illustrated how the nesting jaws can beconfigured correspondingly differingly, however, for testing a weld 17of round cross-section. In this case the nesting jaws 22, 23 as shownare flat and comprise microserrations to prevent the weld 17 to betested from slipping out of place. These microserrations in the form ofgrooves, notches or scorings in the nesting jaws 22, 23 must not, ofcourse, cause any notching in the weld 17 to be tested.

Referring now to FIG. 10 there is illustrated yet a further aspect ofthe jaws for a weld 17 having a round cross-section or of some othershape. In this case the nesting jaws 24, 25 are configured convex tonest the weld 17 to be tested at two opposing narrow shell surfacesegments. Advantageously, the two nesting jaws 24, 25 comprise amicroserration or the like to prevent the weld 17 to be tested fromslipping out of place. The radii of the nesting jaws 24, 25 in this casecan be selected relatively freely, but it is good practice to selectthem at least as large or larger than the radius of the weld 17 to betested.

Referring now to FIG. 11 there is illustrated in conclusion the shape ofthe jaws for a weld 18 having a triangular cross-section. In theembodiment as shown in this case one nesting jaw 26 is configuredconvex. The other nesting jaw 27 comprises, as already explained, awedge shape. The weld 18 to be tested is nested in this case by onelongitudinal edge at the wedge-shaped nesting jaw 27. The opposing flatside of the weld 18 is held by the convex nesting jaw 26.

Referring now to FIG. 12 there is illustrated in perspective how theweld 3 to be tested is to be nested in the jaws. The weld shown in thiscase is made up of three merging, stripped strands 2 of electricalconductors 1. In the ultrasonic welding method the single wires 6 of thestrands 2 are crimp-welded in a square cross-section over a length L.The weld in this case is thus an end weld. The weld 3 is then placed inthe two opposing wedge-shaped nesting jaws 11 (only one of which isshown). Each nesting jaw has a length LS which in this case is smallerthan the length of the weld 3. However, the length LS may also be thesame as the length L of the weld. The weld 3 of square cross-section isnested by the wedge-shaped nesting jaws 11 at two opposing longitudinaledge portions, to which a testing force is applied. Optimally in thiscase the testing force is introduced only into the very narrowlongitudinal edge portion of the weld diagonally.

An end weld 3 tested as an example was approx. 15 mm long. It had aheight of 2.1 mm and a width of 2.8 mm. The ram and anvils of theultrasonic welding machine were 6.5 mm long. The testing force fortesting the weld 3 comprising the dimensions and features as describedabove to be applied via the wedge-shaped nesting jaws 11, 12 was 1,000N. No change was observed in the weld 3 on applying the testing force of1,000 N. Thus the weld could be assessed as sufficient and satisfactory.Any incorrect welding of the weld would have produced a discerniblechange or damage in the weld at a testing force of already 600-700 N,i.e. by the “uncoiling” effect occurring.

As already indicated in the background description it is of course justas possible to already apply the testing force by means of two or morenesting jaws directly after welding in the ultrasonic welding machine.

What is claimed is:
 1. A method of non-destructively testing a weldedassembly, the welded assembly comprising a plurality of strands ofelectrical conductors which are joined together into a bundle byultrasonic welding, the method including the step of introducing adefined testing force into at least two shell surface segments of saidwelded assembly, the testing force being introduced into the at leasttwo shell surface segments in directions which are orientedsubstantially towards each other or in directions which aresubstantially oriented towards a common intersection.
 2. The method asset forth in claim 1, wherein said defined testing force is applied as auniform load substantially along shell lines or narrow shell surfacesegments of said welded assembly.
 3. The method as set forth in claim 1,wherein said testing force is increased continuously from a low startingvalue to a defined testing force.
 4. The method as set forth in claim 3,wherein said increase is linear.
 5. The method as set forth in claim 1,wherein said testing force is 2.5 to 1.25 times higher than the forcewhich, in case of a defective welded assembly, results in a discerniblealteration of the welded assembly.
 6. The method as set forth in claim1, wherein said welded assembly has a polygonal cross-section and saiddefined testing force is introduced at least at two opposinglongitudinal edges of the cross-section.
 7. The method as set forth inclaim 6, wherein said defined testing force is applied at diagonallyopposed longitudinal edges of the cross-section.
 8. The method as setforth in claim 1, wherein said welded assembly has an odd-numberpolygonal cross-section and said defined testing force is introducedalong at least one longitudinal edge of the cross-section and a shellsurface portion opposing this longitudinal edge.
 9. The method as setforth in claim 1, wherein said welded assembly has an ellipticalcross-section and said defined testing force is introduced at shellsurface segments opposing each other in the region of the main orancillary apex of the cross-section.
 10. The method as set forth inclaim 1, wherein said welded assembly has a symmetrical cross-sectionand said defined testing force is introduced at shell surface segmentsopposing each other in the region of the axis of symmetry of thecross-section.
 11. The method as set forth in claim 1, wherein saiddefined testing force is introduced over a partial length of said weldedassembly amounting to at least 20% of the total length of said weldedassembly.
 12. A testing apparatus for non-destructive testing a weldedassembly, the welded assembly comprising a plurality of strands ofelectrical conductors which are joined together into a bundle byultrasonic welding, said apparatus comprising: two or more nesting jawsmovable in directions which are oriented substantially towards eachother or towards a common intersection, each of the jaws being formed sothat a welded assembly to be tested is nested along a shell surfacesegment, and a means for squeezing said nesting jaws together with adefined testing force which is so high that no damage results with afaultless welded assembly, whereas a discernible alteration occurs in adefective welded assembly.
 13. The testing apparatus as set forth inclaim 12, wherein at least one of said nesting jaws having the shape ofa wedge at said side for nesting said welded assembly, the interiorangle of said wedge being greater than the outer angle of saidlongitudinal edge portion of said welded assembly which is to be nestedby said nesting jaw.
 14. The testing apparatus as set forth in claim 12,wherein the inner surface areas of at least one nesting jaw, whichsurface faces the wedged assembly to be nested, comprises severalgrooves oriented parallel to each other.
 15. The testing apparatus asset forth in claim 12, wherein the inner surface area of at least onenesting jaw, which surface faces the wedged assembly to be nested, isconfigured concave.
 16. The testing apparatus as set forth in claim 12,wherein the inner surface area of at least one nesting jaw, whichsurface faces the wedges assembly to be nested, is configures convex.17. The testing apparatus as set forth in claim 12, wherein the innersurface areas of at least one nesting jay, which surface faces thewedges assembly to be nested, is configured substantially flat, saidsurface being machined serrated with grooves, depressions or ridges. 18.The testing apparatus as set forth in claim 12, wherein a means oflimiting sadi testing force is provided which restricts said testingforce to be applied as a maximum.
 19. The testing apparatus as set forthin claim 12, wherein a sensing means is provided for sensing saidalteration occurring in case of a defective welded assembly.
 20. Thetesting apparatus as set forth in claim 19, wherein said sensing meansis a displacement sensor.
 21. The testing apparatus as set forth inclaim 19, wherein said sensing means is a force sensor.
 22. The testingapparatus as set forth in claim 19, wherein an indicator is providedwhich outputs an audible or visual alert on the basis of an error signaloutput by said sensing means.
 23. The testing apparatus as set forth inclaim 12, wherein it is configured as a pliers for manual or pneumaticor hydraulic actuation.
 24. An ultrasonic welding machine for welding aplurality of strands of electrical conductors each made up of singlewires into a bundle of polygonal, round or oval cross-section,comprising a test apparatus as set forth in claim 12.